(1) Field of the Invention
This invention relates to the formation of molded stiffeners which are formed at the same time molded circuit elements are formed.
(2) Description of the Related Art
The processing of molded flexible circuit assemblies requires the use of stiffeners to provide adequate rigidity of the flexible assembly during processing. This invention describes the use of a molded stiffener to accomplish the required rigidity.
U.S. Pat. No. 5,635,671 to Freyman et al. describes encapsulation of an electronic device using injection molding with a two piece mold using a degating region having a material chosen such that the material in the degating region forms a weak bond with the encapsulant used.
U.S. Pat. No. 5,506,756 to Haley describes a ball grid array package containing an integrated circuit die that is directly mounted to either a heat sink or a printed circuit board.
U.S. Pat. No. 5,241,133 to Mullen, III et al. describes a leadless pad array chip carrier package. A semiconductor device is electrically wire bonded and attached with conductive adhesive to a metallized pattern on a printed circuit board.
Flexible circuits are frequently used in electronic circuit packaging. Molded flexible circuit elements are formed on a flexible tape so that several such circuit elements can be processed simultaneously for such operations as electronic chip attachment, wire bond attachment, and encapsulation. Stiffeners are required to provide adequate rigidity to the flexible circuits for these processing operations.
FIGS. 1 and 2 show a number of flexible circuit elements 12 formed on a flexible tape 10. The detail of the circuit elements 12 is not shown here but the circuit elements typically include a die in a molded encapsulation. A stiffener 14 is attached to the assembly to provide rigidity during the processing operations. These flexible circuit assemblies must use a stiffener 14 to add rigidity during these processing operations and this stiffener which must be removed at the last operation of the process, adding cost and complexity.
It is a principle objective of this invention to provide a method of forming molded flexible circuits which includes a molded stiffener and do not require an additional stiffener to be attached.
It is another principle objective to this invention to provide molded flexible circuits which include molded stiffeners and do not require additional stiffeners to be attached.
These objectives are achieved by using a mold section to form flexible circuit elements on a flexible tape. The mold section includes circuit element cavities, a stiffener cavity, mold runner cavities, and a molding compound cull block. Uncured molding compound is placed in the molding compound cull block and flowed through the mold runner cavities into the circuit element cavities and the stiffener cavity. The molding compound is cured and the mold section removed leaving molded circuit elements and stiffeners formed on the flexible tape. The molded circuit elements, which will be explained in more detail later, include a circuit die and wiring.
The molded stiffeners provide adequate stiffening for subsequent processing operations and no additional stiffeners are required. The molded stiffeners can be used in the processing and are removed when the molded circuit elements are removed from the flexible tape.